One of the biggest reasons why the Pirates were able to make the playoffs last year was that their pitching staff gave up very few home runs (#1 in fewest allowed with 101). Even in the 2nd half when they became hittable (falling from 1st in batting average against to 17th), they still managed to lead the league in fewest home runs allowed.
In 2014, they're pitching very well so far, with the 7th best ERA in the ML (2.66). It's early, but they are allowed more home runs than at the end of last year, ranking only 19th in fewest HR allowed.
It might be nothing to worry about even if it persists because they didn't become really stingy until after April last year.